System Bits: Nov. 29

Qubit device fabbed in standard CMOS
In a major step toward commercialization of quantum computing, Leti, an institute of CEA Tech, along with Inac, a fundamental research division of CEA, and the University of Grenoble Alpes have achieved the first demonstration of a quantum-dot-based spin qubit using a device fabricated on a 300-mm CMOS fab line.

Maud Vinet, Leti’s advanced CMOS manager said, “This proof-of-concept result, obtained using a CMOS fab line, is driving a lot of interest from our semiconductor industrial partners, as it represents an opportunity to extend the impact of Si CMOS technology and infrastructure beyond the end of Moore’s Law.”

The proof-of-concept breakthrough uses a device fabricated on a 300-mm CMOS fab line consisting of a two-gate, p-type transistor with an undoped channel. At low temperature, the first gate defines a quantum dot encoding a hole spin qubit, and the second one defines a quantum dot used for the qubit readout. All electrical, two-axis control of the spin qubit is achieved by applying a phase-tunable microwave modulation to the first gate, the team explained.

They reminded that semiconductor spin qubits reported so far have been realized in academic research facilities, but this one was done with FDSOI field-effect transistors. The standard single-gate transistor layout is modified in order to accommodate a second closely spaced gate, which serves for the qubit readout.

Another key innovation lies in the use of a p-type transistor, meaning that the qubit is encoded by the spin of a hole and not the spin of an electron. This specificity makes the qubit electrically controllable with no additional device components required for qubit manipulation, the researchers noted.

The one-qubit demonstrator brings CMOS technology closer to the emerging field of quantum spintronics.

(a) Simplified three-dimensional schematic of a silicon-on-insulator nanowire field-effect transistor with two gates, gate 1 and gate 2. Using a bias tee, gate 1 is connected to a low-pass-filtered line, used to apply a static gate voltage Vg1, and to a 20 GHz-bandwidth line, used to apply the high-frequency modulation necessary for qubit initialization, manipulation and read-out. (b) Colourized device top view obtained by scanning electron microscopy just after the fabrication of gates and spacers. Scale bar, 75 nm. (c) Colourized transmission electron microscopy image of the device along a longitudinal cross-sectional plane. Scale bar, 50 nm.
(Source: CEA Leti)

Vinet added: “This proof-of-concept result, obtained using a CMOS fab line, is driving a lot of interest from our semiconductor industrial partners, as it represents an opportunity to extend the impact of Si CMOS technology and infrastructure beyond the end of Moore’s Law. The way toward the quantum computer is still long, but CEA is leveraging its background in physics and computing, from technology to system and architecture, to build a roadmap toward the quantum calculator.”

Photonic crystals reveal internal characteristics
A new technique developed by MIT researchers reveals the inner details of photonic crystals, which are synthetic materials whose exotic optical properties are the subject of widespread research.

While photonic crystals are generally made by drilling millions of closely spaced, minuscule holes in a slab of transparent material, using variations of microchip-fabrication methods, depending on the exact orientation, size, and spacing of these holes, these materials can exhibit a variety of peculiar optical properties, including “superlensing,” which allows for magnification that pushes beyond the normal theoretical limits, and “negative refraction,” in which light is bent in a direction opposite to its path through normal transparent materials.

To understand exactly how light of various colors and from various directions moves through photonic crystals, however, requires extremely complex calculations and researchers often use highly simplified approaches, i.e., they may only calculate the behavior of light along a single direction or for a single color. But the new MIT technique makes the full range of information directly visible allowing researchers to use a straightforward laboratory setup to display the information — a pattern of so-called “iso-frequency contours” — in a graphical form that can be simply photographed and examined, in many cases eliminating the need for calculations.

This image shows theoretical (right) and experimental (left) iso-frequency contours of a photonic crystal slabs superimposed on each other. (Source: MIT)

The finding could potentially be useful for a number of different applications such as leading to a way of making large, transparent display screens, where most light would pass straight through as if through a window, but light of specific frequencies would be scattered to produce a clear image on the screen. Or, the method could be used to make private displays that would only be visible to the person directly in front of the screen.

And because it relies on imperfections in the fabrication of the crystal, this method could also be used as a quality-control measure for manufacturing of such materials; the images provide an indication of not only the total amount of imperfections, but also their specific nature — that is, whether the dominant disorder in the sample comes from noncircular holes or etches that aren’t straight — so that the process can be tuned and improved, the team noted.

IoT device biosignal measuring
Daegu Gyeongbuk Institute of Science & Technology in Korea said Professor Kyung-in Jang’s research team from the Department of Robotics Engineering has developed bio-signal measuring electrodes that can be mounted on IoT devices through joint research with a research team led by professor John Rogers of the University of Illinois.

The bio-signal measuring electrodes developed by the research team can be easily mounted on IoT devices for health diagnosis, thus they can measure bio-signals such as brain waves and electrocardiograms without additional analysis and measurement equipment while not interfering or restricting human activities.

The team reminded that conventional hydro-gel based electrodes required external analysis and measurement devices to measure bio-signals due to their pulpy gel forms, which made their attachment to and detachment from IoT devices instable. In addition, since these electrodes were wet-bonded to the skin, there have been disadvantages that the characteristics of the electrodes deteriorated or their performance decreased when the electrodes were dried in the air over a long period.

In contrast, the electrodes developed by Professor Kyung-in Jang can be easily interlocked as if they are a part of IoT devices for health diagnosis. Also, since they are composed only of polymer and metal materials, they have the advantage of there being no possibility of drying in the air.

DGIST Professor Kyung-in Jang’s research team from the Department of Robotics Engineering has developed bio-signal measuring electrodes that can be mounted on IoT devices through joint research with a research team led by professor John Rogers of the University of Illinois. (Source: DGIST)